Glass melters, or furnaces, for use in the manufacture of glass fibers, are old and well-known throughout the art. For example, see U.S. Pat. Nos. 4,017,294 and 4,023,950.
The '294 patent generally describes an open-top electric melter, or furnace, having a central bottom discharge outlet. The melter includes a ceramic lining and a molybdenum outlet member located at the bottom of the melter, at the center thereof. The tapping block of the outlet is made of molybdenum, a material which is able to withstand high temperatures within the furnace and is substantially corrosion resistant. Unfortunately, glass melters which include outlets located at the bottom center of the melter, as in the '294 patent, have been found to suffer from a number of problems, some of which are discussed below.
The bottom center of an electric open-top glass melter experiences the highest temperatures in the melter (e.g. from about 3,1000-3,2000.degree. F. in some electric melters). The rate of corrosion of outlet structures is temperature related. Accordingly, due to oxides found in the glass batch, molybdenum center outlets, such as that disclosed in the '294 patent, tend to wear out quicker than do refractory linings provided on the sidewalls and bottom of such furnaces. In such cases, because the outlet needs to be replaced prior to the refractory lining material, the furnace must be shut down for repairs more often. For example, assuming that the refractory lining in such an electric melter needs to be replaced approximately once a year, the molybdenum center outlet which wears out at a more rapid rate would have to be replaced every six months or so, thereby necessitating twice as many shutdowns of the furnace than would be needed if the refractory and outlet structure wore out, and could be replaced, at the same time. Each time a melter in a fiberglass manufacturing plant is shut down in order to replace either the outlet structure or the refractory lining, production and output suffer. This is undesirable.
U.S. Pat. No. 4,001,001 discloses a combination gas and electric furnace that is horizontal in design (i.e. the melter and refiner are at substantially the same level) and adapted for melting glass batch materials in part by the application of heat from overhead flames within the furnace. This furnace includes electric heating electrodes submerged within the batch material and gas fueled flame firing ports located in the atmosphere at an elevation above the batch. The atmosphere above the batch is heated by these flames so that the entire glass batch, including the top surface of the batch, within the melter is melted into molten form (i.e. no hardened or quasi-solid glass batch is present on the top surface of the batch as it flows into the refiner).
Unfortunately, the melter of the '001 patent suffers from a number of problems, some of which are set forth below. The melter of the '001 patent is a combination gas-electric melter, including a closed-top (i.e. hot-top) which keeps the atmosphere within the melter, above the glass batch, at a heightened temperature in order to melt the glass on the top surface of the batch. These types of melters are often viewed as inefficient with regard to energy consumption. Furthermore, this type of melter requires that the top surface of the glass batch be in molten form prior to entry into the refiner so that the spinners do not become clogged (i.e. there is no structure to prohibit entry of quasi-hardened batch on the top surface from flowing into the refiner). The atmosphere heating requirement is undesirable, very costly, and inefficient. Still further, the furnace of the '001 patent does not typically heat the batch to the extreme temperatures of electric open-top melters, and thus does not typically need to address the same degree of erosion problems associated with high temperature electric open-top melters.
U.S. Pat. No. 4,405,351 discloses another hot-top, or closed-top, gas-fueled melter or furnace used in the manufacture of glass fibers. Unfortunately, the melter of the '351 patent suffers from at least the same problems discussed above relative to the '001 patent, in that: (i) its low operating temperatures (up to 2,600.degree. F.) do not render it susceptible to the erosion problems associated with the much higher batch temperatures of electric open-top furnaces; (ii) the fuel-air method of heating and melting the batch in the '351 patent is often inefficient and undesirable; and (iii) the throat or side outlet through which the molten glass flows into the refiner would erode much too quickly if exposed to the higher temperatures of electric furnaces. For example, if the throat (typically made of refractory material which can withstand. the heat generated in a gas furnace) in the '351 patent was exposed to temperatures on the order of from about 2,700-3,200.degree. F., it would break down/erode, especially upwardly, due to "upward drilling" of the throat. However, because the temperatures maintained within the batch in the gas melter of the '351 patent are so low, this problem is not addressed therein.
In view of the above, it is readily apparent that there exists a need in the art for an electric open-top glass melter, and corresponding method, for use in the manufacture of glass fibers wherein the melter is provided with an outlet or throat structure that wears out at a slower rate than do prior art outlets which are located at the bottom center of the melter, and which prevents solid or quasi-solid glass batch and eroded refractory from flowing from the melter interior toward the forehearth. Still further, there exists a need in the art for a melter that has reduced downtime (i.e. an increase in production results).
It is a purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.